[1]} used a similar idea to Model REF  while only introducing \(\Delta _t\)  in generating synthetic data with a symmetric or asymmetric covariance.
One can clearly see that in Model REF , \(\Delta _s = \Delta _t = 0\)  leads to a fully symmetric random field, \(\Delta _s \ne 0\)  leads to a random field that is not \(\text{V}^\text{sym}\)  or \(\text{S}^\text{sym}\) , and \(\Delta _t \ne 0\)  leads to a random field that is not \(\text{V}^\text{sym}\)  or \(\text{T}^\text{sym}\) .
